1. Field of the Invention
The present invention relates to a transport belt used in an image formation device such as a copying machine, printer, and facsimile, specifically to a transport belt in which the surface of the belt base made of an elastic material is covered with a covering material, and an image formation device using the same.
2. Description of the Related Art
In the image formation device such as a copying machine, printer, and facsimile, a device is already available that forms images on an image retainer such as a photosensitive drum, and transfers the images indirectly to a recording medium through an intermediate transfer belt, or transfers the images directly to the recording medium on a recording medium holding belt.
In this sort of transport belt (intermediate transfer belt, recording medium holding belt), with a view to maintaining the transfer performance of images from the image retainer to a satisfactory condition, it is essential to secure the nipping area between the transport belt and the image retainer and the pressure on the nipping area between the transport belt and the image retainer, and to increase the adherence between them.
To achieve these, a transport belt is already provided that forms the belt base itself of the transport belt with an elastic material such as a flexible rubber material and the like.
In a case of using a rubber material for the belt base, it is a general exercise to add chemicals in the rubber material in order to satisfy the properties such as resistance to ozone, fire resistance, antidegradation, etc.; however, there is a possibility that the added chemicals deposit on the surface of the transport belt, the so-called bleeding phenomenon occurs.
To solve such technological problems, there is already provided a technique that, while exhibiting the resistance to ozone and fire resistance by use of a mixed base material of chloroprene rubber and EPDM as the base material of the transport belt, effectively avoids the bleeding phenomenon (refer to the Patent Reference 1).
The Patent Reference 1 discloses that to disperse acetylene black, furnace black and acetylene black, or acetylene black and Ketjen black in the base material of a belt will repress the fluctuations with time of the electric resistance.
[Patent Reference 1]
Japanese Published Unexamined Patent Application No. Hei 9-179414 (detailed description of the invention)
This type of transport belt generally comes in a form that covers the surface of the belt base with a covering material, prevents degradation of the transport belt, and secures lubricity of the transport belt and so forth.
However, when the surface of the transport belt was put long in tight contact with the surface of the image retainer, the bleeding phenomenon was observed.
This is considered as follows: when the covering layer of the transport belt adheres to the surface of the image retainer, the negative pressure between both causes low-molecular oil compositions inside the belt base (contained in EPDM and various chemicals added during kneading) to deposit on the surface of the transport belt.
In this case, given conductive fine particles are dispersed in the base material of a belt, and these particles contribute to the adjustment of resistance (conductivity); however, they do not work to block the deposition of the low-molecular oil compositions, and they do not exhibit the function to repress the bleeding phenomenon at all. In the covering layer are dispersed a minute amount of a lubricant filler and a conductive filler and so forth. However, these fillers do not show the function to repress the bleeding phenomenon.
In order to avoid such deficiencies, indispensable is a technique that separates the image retainer from the transport belt through a retracting mechanism during non-image formation. However, this system needs to provide the retracting mechanism between both, which involves a technical problem that complicates the construction of the device to that extent.